Various electronic calipers are known that use electronic position encoders. These encoders are generally based on low-power inductive, capacitive, or magnetic position sensing technology. In general, an encoder may comprise a readhead and a scale. The readhead may generally comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale, along a measuring axis. In an electronic caliper the scale is generally affixed to an elongated scale member that includes a first measuring jaw and the readhead is affixed to a slide which is movable along the scale member and which includes a second measuring jaw. Thus, measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead.
Compact electronic hand tool type calipers, (e.g., those having a measurement range on the order of 100-250 mm) have evolved to have a relatively standardized configuration including a refined set of dimensions and ergonomics, as well as extremely low power consumption. Hand tool type calipers that are even slightly larger or heavier than the standardized configuration are generally rejected in the marketplace. In conventional calipers, the elongated scale member typically has a relatively wide top surface and relatively narrow edges. The encoder scale is affixed to the top surface and the readhead is affixed to a surface of the movable slide such that it moves along the top surface over the scale. An appropriate operating gap is provided between the readhead sensor and the scale. Among other advantages, this configuration allows the readhead to be collocated with the display and the other electronic components of the caliper, which is economical. This configuration also allows the use of a relatively large sensing region between the readhead sensor and scale. This is beneficial because the S/N ratio of the types of position encoders used in electronic calipers and typically benefits from increasing the sensing region dimensions for a given operating gap. Thus, this has been the conventional configuration. For example, U.S. Pat. Nos. 6,229,301; 6,724,186; 6,332,278; RE37,490; 5,973,494; and 5,574,381, each of which is hereby incorporated by reference in its entirety, show calipers conforming to this configuration.
U.S. Pat. No. 5,029,402, discloses a slightly different configuration used in an unconventional large caliper-type sliding gauge, which is described as being usable for measuring large objects such as tree trunks, etc. The sliding gauge includes a rod and a slide. The rod is disclosed as having eight sides. The rod includes markings that may be sensed by a length sensor on the slide. FIG. 6 of the '402 patent shows various surfaces where markings and length sensors may be applied, separated by an appropriate operating gap. In some embodiments, the widest surfaces of the rod are not used. However, the disclosure of '402 patent discloses a “caliper” that is not compact, and furthermore offers no clear advantages over the conventional caliper configuration outlined above, for conventional hand tool type caliper applications.
It would be desirable to advance the state of the art of compact hand tool type electronic calipers, and certain related compact “jawless” calipers that comprise similar or identical components used as low cost linear scales. For example, it would be desirable to further lower the cost of electronic calipers, and/or make them more reliable.